This invention relates to inks characterized by light sensitive properties. In the manufacture of litho plates, etching microcircuits, or engraving a cylinder it is necessary to use a light sensitive coating, expose it through a photographic negative or positive to obtain the desired picture or words. Applying a light sensitive coating by jet printer eliminates the need for the photographic negative or positive.
Ink jet printing is a recent development in the art of applying identifying and decorative indicia to a base. In general terms, a fluid ink is forced, under pressure, through a very small orifice in an orifice block which contains a piezoelectric crystal vibrating at high frequency (50-100,000 vibrations per second) causing the ink passing through the orifice to be broken into minute droplets equal in number to the crystal vibrations. The minute droplets are passed through a charging area where individual droplets receive an electrical charge in response to a video signal, the amplitude of the charge being dependent on the amplitude of the video signal. The droplets then pass through an electrical field of fixed intensity, causing a varied deflection of the individual droplets dependent on the intensity of the charge associated therewith, after which the deflected drops are allowed to impinge to the base medium which is to receive the decorative or informative printed indicia. Apparatus suitable for carrying out the ink jet printing process is described in detail in U.S. Pat. Nos. 3,465,350 and 3,465,351, issued Sept. 2, 1969 and it is in connection with an apparatus and process such as are described in the aforementioned patents that the ink of the present invention is designed to function.
In order to operate satisfactorily in an ink jet printing system, an ink must display a consistent drop breakup length, drop velocity and drop charge under set operating conditions.
It has been determined that on ink jet printer, described in U.S. Pat. Nos. 3,465,350 and 3,465,351, inks with viscosity of 25 cps. will perform satisfactorily depending upon the type of nozzle used. However, inks with lower viscosities perform much better. Resistivity of ink may range as high as 10,000 ohm cm. for satisfactory operations.